1. Field of the Invention
The present invention relates to a system and method for draining remaining water in a fuel cell, and in particular, relates to an art for draining remaining water outside, which remains in reaction-gas passages of a fuel cell.
2. Description of the Related Art
In conventional solid polymer electrolyte membrane fuel cells, each cell has an anode and a cathode which are provided on either side of a solid polymer electrolyte membrane. Plural such cells are stacked so as to form a stack, which is called a “fuel cell” in the following explanations. In the fuel cell, hydrogen, which functions as fuel, is supplied to the anode, while air, which functions as an oxidizing gas, is supplied to the cathode. The catalytic reaction on the anode generates hydrogen ions, and the hydrogen ions are transferred to the cathode via an electrolyte membrane. The transferred hydrogen ions react with oxygen on the cathode, thereby generating electric power.
In order to maintain the ion conductivity of the solid polymer electrolyte membrane, water is mixed with each reaction gas (i.e., hydrogen or air) which is supplied to the fuel cell, by using a humidifier or the like. In addition, when the fuel cell works, water is produced due to an electrochemical reaction. If such water condenses in a reaction gas passage (through which each reaction gas passes), the condensed water may remain in the reaction gas passage, so that the passage may be blocked.
If the fuel cell operation is stopped and the temperature of the fuel cell falls below the freezing point while the reaction gas passage is blocked by the condensed water, then the condensed water freezes which blocks the gas passage. Therefore, it is difficult to restart the fuel cell.
In order to solve such a problem, Published Japanese Translation No. 2000-512068, of PCT International Publication No. WO97/48142, discloses a fuel cell power generating system in which the inside of the reaction gas passage is purged while the fuel cell is stopped, so that the remaining water in the reaction gas passage is drained outside. This system employs a dedicated gas supply passage for purging, where a dried purification gas passes through the gas supply passage. Accordingly, the remaining water in the reaction gas passage is drained outside.
However, if a dedicated gas supply line is provided as in the above conventional fuel cell power generating system, the system structure is complicated. In addition, passing of the dried purification gas produces an excessively dried state inside the fuel cell, so that the solid polymer electrolyte membrane may be damaged.